1. Field of the Invention
The present invention relates to a method for in situ treatment of water and soil which has been contaminated with chlorinated hydrocarbons. Aerobic methods employing an oxygen source, nutrients and indigenous microorganisms without the addition of a flammable carbon source such as propane or methane gas are used.
2. Related Art and Summary of Invention
Contamination of soil, groundwater, and subterranean formations as a result of hydrocarbon spills has presented a serious environmental problem. Various methods have been employed to remedy the problem. These include air stripping; vacuum venting; pump-and-treat operations using carbon adsorption or steam stripping, for example; and excavation. None of these methods takes care of the soil and water at the same time. Recently, several in situ techniques have been employed for some types of hydrocarbon spills.
U.S. Pat. No. 3,846,290 to Raymond, which is incorporated herein by reference, teaches a process for eliminating hydrocarbon contaminants such as crude oil and gasoline from underground water sources by providing nutrients and oxygen for indigenous microorganisms. The nutrients and oxygen are introduced through wells within and adjacent to the contaminated area, and water is removed from the area by other wells until the hydrocarbons are reduced to an acceptable level.
U.S. Pat. No. 4,401,569 to Jhaveri et al., which is incorporated herein by reference, teaches a process for treatment, both in situ and outside the earth, of hydrocarbons and halogenated hydrocarbons, in particular methylene chloride, by removing the ground water from the contaminated area; treating it with microorganisms, nutrients, and gases such as oxygen, nitrogen, and carbon dioxide; and returning it to the ground optionally together with other nutrients and oxygen.
U.S. Pat. No. 4,588,506 to Raymond et al., which is incorporated herein by reference, teaches a process for treatment of contaminants which may include inorganic materials and organic materials such as petroleum products, phenols, halo-carbons, and alcohols. Hydrogen peroxide at relatively low concentrations is injected into the subterranean formation. The concentration is gradually increased so as to acclimate the biota within the formation so that they can tolerate higher concentrations of hydrogen peroxide to, in turn, increase the rate of oxidation of the contaminants. Periodically the concentration of hydrogen peroxide is increased to a toxic level to remove the biota and any biomass and increase the permeability of the formation at the site of hydrogen peroxide injection.
Certain contaminants have been reported as not being satisfactorily treated by the aerobic in situ techniques, however. For example, chlorinated aliphatics such as 1,1,1- and 1,1,2-trichloroethane, 1,1-and 1,2-dichloroethane, trichloroethylene, carbon tetrachloride, tetrachloroethylene, chloroform, 1,2-dichloroethylene, and cis- and trans-1,2-dichloroethylene have been reported as not being biodegradable under aerobic processes. Also, under anaerobic conditions chlorinated aliphatic compounds such as trichloroethylene and tetrachloroethylene will metabolize to vinyl chloride, which is undesirable due to the reported carcinogenic nature of vinyl chloride.
Bouwer, Rittmann and McCarty in Volume 15 (1981) of Environmental Science Technology. pages 596-599, describe both aerobic and anaerobic tests for biodegradation of chloroform, trichloroethylene, tetrachloroethylene, dibromomethylene, dibromochloromethane and bromodichloromethane. They conclude there are no aerobic conditions under which these compounds degrade. Under anaerobic conditions, they note increased rates over those observed with the sterile controls indicating a microbial role in the disappearance of these compounds under anaerobic conditions.
Wood, Lang and Payan, in the 1985, edition of Ground Water Quality, J. Wiley and Sons, Inc., teach that anaerobic degradation of trichloroethylene and tetrachloroethylene can lead to highly volatile intermediates such as vinyl chloride, 1,1-dichloroethene and cis- and trans-1,2-dichloroethene depending on the microbial profile, which will vary seasonally.
Particularly, since these halogenated aliphatic hydrocarbons have found wide use as industrial degreasers, dry cleaning agents and septic tank cleaners, the potential for spills is great and, indeed, has been realized. As such, much effort has gone into finding an effective cleanup procedure for these compounds.
Recently, scientists have taught that it was possible to biodegrade trichloroethylene if a highly flammable carbon source such as methane or propane were co-fed with the air and nutrients. For example, B. H. Wilson and M. V. White presented a paper at the May, 1986, National Well Water Association Symposium in Columbus, Ohio, in which they taught that trichloroethylene in contaminated water could be reduced by the introduction of propane or natural gas and air into a coarse sand column through which the water was flowing. But there was no loss of 1,1,1-trichloroethane under the same conditions.
J. T. Wilson presented another paper at the June, 1986, Standford University Seminar on Biological Approaches to Aquifer Restoration in which he compared aerobic and anaerobic degradation of chlorinated aliphatic hydrocarbons. Current efforts to add propane or natural gas were discussed.
An object of the current invention is to avoid the formation of the undesirable vinyl chloride by employing an aerobic process while at the same time avoiding the need for employing a highly flammable carbon source as a co-feed.